I think the best all-around fly fishing podcast is Tom Rosenbauer from Orvis. In this episode from last fall, he interviews a geologist.
Geology & Trout Streams
https://orvisffguide.libsyn.com/how-land-use-and-geology-affect-mountain-streams-with-dr-nelson-ham
There were two takeaway messages for me:
First, when humans have “disturbed” or altered a stream, our ideas about “restoration” may not make sense. We don’t necessarily have a good image of what the stream was in the past, much less the distant past. Its all more complex than I used to imagine.
Second, if the “base flow index” is less than X, then the stream likely won’t hold trout. I didn’t really know anything about “base flow index” so it was a good intro to me of the subject.